This application claims the priority of German patent application No. 198 13 674.9, filed Mar. 27, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a device for heating and cooling a compartment of a motor vehicle powered by an internal combustion engine. The device has a coolant circuit with a compressor, an ambient heat exchanger, at least one expansion device, an interior air heat exchanger, and an exhaust heat exchanger that can be heated by exhaust gases from the internal combustion engine. A coolant is capable of being guided, during a heating operation, through the compressor and, while giving off heat, through the internal heat exchanger connected downstream from the compressor. A method for operating the device for heating and cooling the motor vehicle compartment is also disclosed. In the method, a coolant is compressed and heated in the compressor during heating and is then cooled in the interior heat exchanger.
A device of the type mentioned above for motor vehicles is known from DE 33 18 025 A1. This device includes an evaporator that is heated by the exhaust from an internal combustion engine. The evaporator is connected in series with an expansion valve which is operable only as long as the exhaust heat from the internal combustion engine has a specified value. In addition, a compressor is provided in this air conditioner and undergoes a reduction in rpm to a value different from zero when the effective cross section of the expansion valve changes. Heating operation takes place in three stages in this air conditioner. In the first stage, shortly after starting the motor vehicle, the compressor compresses the coolant and delivers it through a four-way valve to the evaporator where heat exchange takes place from the coolant to the air in the compartment that is flowing into the compartment. When exhaust heat from the engine is sufficient, a bypass line containing an exhaust heat exchanger is cut in by actuating a three-way valve. As a result, the exhaust heat from the engine supplies the heat required to the interior. This is followed by a conventional heating operation with an air-coolant heat exchanger to which the coolant from the engine is supplied. In this third stage, the bypass line is cut out again. Initially, the expansion valve is closed and the coolant that is in the bypass line is heated with the aid of the compressor.
The disadvantage of this known solution, however, is that the three-stage heating operation of the air conditioner requires a high construction and regulating-engineering cost.
A device is also known from DE 34 43 899 C2 for heating and cooling a compartment of a motor vehicle powered by an internal combustion engine. In this known device, if the compartment air is to be heated, the coolant is fed downstream from the compressor through a coolant switch into a parallel bypass line containing the condenser and expansion device. In this bypass line, the coolant is heated by the intermediate air in a heat exchanger by a closed intermediate air circuit. In the heat exchanger in the intermediate air circuit, the intermediate air delivered by a blower is heated by the exhaust stream from the engine.
The disadvantage of this arrangement, in addition to the complexity of the described solution, is that an auxiliary mass flow must be heated for heat transfer and only a portion of the heat is transferred in a useful manner. Moreover, the volume of heat, which is small in engines that have been optimized for efficiency, is further reduced in the exhaust by unavoidable transfer losses and is transferred only after a delay because of the thermal mass of the additional components involved.
Hence, the goal of the present invention is to increase the power transferred by the coolant circuit to the compartment air in vehicles, especially in consumption-optimized vehicles such as Diesel vehicles, completely and directly following starting, and to increase the efficiency of a device for heating and cooling and shorten its response time.
According to the invention, this goal is achieved by connecting a compressor, an interior heat exchanger, an expansion device, an ambient heat exchanger, and an exhaust heat exchanger in series so that, for a heating operation, the coolant is expandable in the expansion device to a temperature below an intake temperature of the coolant into the compressor, exposed in the ambient heat exchanger to warmer ambient air, heated in the exhaust heat exchanger by the exhaust gases from the internal combustion engine, and compressed in the compressor. For cooling, the compressor, the ambient heat exchanger, the expansion device, and the internal heat exchanger are connected in series, and the coolant is exposed, in the ambient heat exchanger, to colder ambient air and expanded in the expansion device to a temperature below a compartment air temperature. The compartment air is exposed to the coolant in the internal heat exchanger. Heating, in other words, is accomplished by successively expanding the coolant in the expansion device to a temperature below an intake temperature of the coolant into the compressor, exposing the coolant in the ambient heat exchanger, to ambient air, heating the coolant, in the exhaust heat exchanger, by exhaust gases from the internal combustion engine, and compressing the coolant in the compressor. For cooling, the coolant is successively exposed to colder ambient air in the ambient heat exchanger and expanded in the expansion device to a temperature below a compartment air temperature. The compartment air is exposed, in the interior heat exchanger, to the coolant.
When the device is used to heat a compartment of a motor vehicle, the coolant is successively expanded in an advantageous manner in the expansion device to a temperature below an intake temperature of the coolant into the compressor, exposed to ambient air in the ambient heat exchanger, heated in the exhaust heat exchanger by the exhaust from the engine, compressed in the compressor, and exposed to cold vehicle internal chamber air in the internal chamber heat exchanger. The vehicle interior is heated by the vehicle interior air heated in the interior heat exchanger.
As a result of the series connection of the components according to the invention, a thermodynamic cyclic process is made possible in which the heating and cooling power can be made available in a sufficient quantity under nearly all operating conditions of the engine. The coolant mass flow is radiated by the compressor as a function of the necessary heating or cooling power in such fashion that the coolant mass flow required for power to be absorbed or delivered is available at the interior heat exchanger.
The coolant mass flow is largely independent of the processor pressure in the circuit, so that the device, even with a low or high power requirement, can be operated steadily in a range with high efficiency. A regulating range of the heating or cooling power from zero to a maximum value that can be achieved within a technically feasible scope with a high efficiency of the device can be achieved.
With the method according to the invention, the mass flow of the coolant is varied as necessary as a function of the required heating power and the quantity of heat supplied from the environment and the exhaust heat of the engine so that the air conditioner permanently installed for cooling in summer can be used in a simple fashion for heating the interior of the motor vehicle on cold days.